Method for fabricating a semiconductor device including using a hard mask or a silylated photoresist for an angled tilted ion implant

Abstract

A hard mask 21 a which has an opening for exposing a p-type region 2 defined in a silicon substrate 1 and is made of, for example, a BPSG film is formed. Then, the hard mask 21 a is subjected to isotropic etching using argon gas, to have its edge rounded off, thereby forming an implantation hard mask 21 having a tapered edge. Subsequently, large-angle-tilt ion implantation of an n-type impurity is performed using the implantation hard mask 21 as a mask, thereby forming an n − layer 13 having an LDD structure. Thereafter, the implantation hard mask 11 is removed. In this manner, it is possible to perform large-angle-tilt ion implantation using an implantation mask thinner than a conventional implantation mask.

What is claimed is:  
     
       1. A method for fabricating a semiconductor device, the method comprising the steps of: 
       a) forming a gate insulating film and a gate electrode over a first transistor region defined in a semiconductor substrate;  
       b) forming, on the semiconductor substrate, a hard mask having an opening for exposing the first transistor region therein, after the step a) has been performed;  
       c) implanting an impurity into the semiconductor substrate in the manner of large-angle-tilt ion implantation, using the gate electrode and the hard mask as a mask for ion implantation; and  
       d) removing the hard mask, after the step c) has been performed,  
       wherein a second transistor region is provided at a side of the first transistor region in part of the semiconductor substrate with an insulating film for transistor isolation interposed therebetween, and  
       in the step b), the hard mask is formed to cover the second transistor region.  
     
     
       2. The method of  claim 1 , wherein in the step b), the thickness of the hard mask and the width of the opening of the hard mask are defined such that the impurity reaches a region under the gate electrode during the large-angle-tilt ion implantation in the step c). 
     
     
       3. The method of  claim 1 , wherein the hard mask is one out of a BPSG film, a PSG film and a silicon nitride film. 
     
     
       4. A method for fabricating a semiconductor device, the method comprising the steps of: 
       a) forming a gate insulating film and a gate electrode over a first transistor region defined in a semiconductor substrate;  
       b) forming, on the semiconductor substrate, a hard mask having an opening for exposing the first transistor region therein, after the step a) has been performed;  
       c) implanting an impurity into the semiconductor substrate in the manner of large-angle-tilt ion implantation, using the gate electrode and the hard mask as a mask for ion implantation;  
       d) removing the hard mask after the step c) has been performed; and  
       e) rounding off an upper edge of the hard mask, thereby making the hard mask to have a tapered edge, between the steps b) and c).  
     
     
       5. The method of  claim 4 , wherein in the step e), isotropic etching is performed, thereby making the hard mask to have the tapered edge. 
     
     
       6. The method of  claim 4 , wherein in the step e), heat treatment is performed, thereby making the hard mask to have the tapered edge. 
     
     
       7. A method for fabricating a semiconductor device, the method comprising the steps of: 
       a) forming a gate insulating film and a gate electrode over a first transistor region defined in a semiconductor substrate;  
       b) forming a resist layer on the semiconductor substrate;  
       c) silylating at least part of the resist layer other than a region of the resist layer located on the first transistor region, thereby forming a silylated region;  
       d) removing at least part of the region of the resist layer other than the silylated region, thereby forming a silylated resist pattern; and  
       e) implanting an impurity into the semiconductor substrate in the manner of large-angle-tilt ion implantation, using the silylated resist pattern as a mask for ion implantation.  
     
     
       8. The method of  claim 7 , including the step of oxidizing the silylated region, between the steps d) and e). 
     
     
       9. The method of  claim 4 , wherein the hard mask is one of a BPSG film, a PSG film and a silicon nitride film.